Process of separating/purifying pentafluoropropane

ABSTRACT

There is provided an azeotropic mixture having 1,1,1,3,3-pentafluoropropane and hydrogen fluoride. Further, there is provided a process of separating/purifying R-245fa and/or HF from a mixture of R-245fa and HF wherein the mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride is subjected to a distillation step so that a distillate is obtained which has the azeotropic mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride, and a bottom product is obtained which has separated/purified 1,1,1,3,3-pentafluoropropane or hydrogen fluoride.

This application is a divisional of co-pending application Ser. No.09/101,809, filed on Jul. 23, 1998 and for which priority is claimedunder 35 U.S.C. §120. Application Ser. No. 09/101,809 is the nationalphase of PCT International Application No. PCT/JP97/00134 filed on Jan.22, 1997 under 35 U.S.C. §371. The entire contents of each of theabove-identified applications are hereby incorporated by reference. Thisapplication also claims priority of Application No. 8-009085 and8-156701 filed in Japan on Jan. 23, 1996 and Jun. 18, 1996, respectivelyunder 35 U.S.C. §119.

This application claims the benefit under 35 U.S.C. §371 of prior PCTInternational Application No. PCT/JP97/00134 which has an Internationalfiling date of Jan. 22, 1997 which designated the United States ofAmerica, the entire contents of which are hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to an azeotropic mixture of 1, 1, 1, 3,3-pentafluoropropane (which hereinafter may be referred to as also“R-245fa”) and hydrogen fluoride (which hereinafter may be referred toas also “HF”), and a process of separating/purifying R-245fa and/orhydrogen fluoride from a mixture comprising at least R-245fa andhydrogen fluoride.

BACKGROUND ART

R-245fa is a useful compound which can be used for an alternative forCFC (chlorofluorocarbon) or HCFC (hydrochlorofluorocarbon) used as acooling medium and a foaming agent and which is not likely to destroythe ozone layer.

R-245fa can be produced by fluorination of 1, 1, 1, 3,3-pentachloropropane using HF. In this production process, since anexcessive amount of HF is used for the reaction, a reaction mixturecontains a considerable amount of unreacted HF in addition to producedR-245fa, and also may contain, in addition to these, a by-product (forexample, R-244fa (1, 1, 1, 3-tetrafluoro-3-chloropropane) and so on). Acomposition of such a reaction mixture is determined by reactionconditions, and in order to obtain R-245fa from the reaction mixture asdescribed above, the mixture is subjected to separation/purification.Further, it is desirable to recover the unreacted HF from the reactionmixture and re-used for the reaction.

In the present specification, the term “separate/purify” is intended tomean such that when a mixture stream comprising specific two components(for example, R-245fa and HF) is subjected to a certain processing step(for example, a distillation step) and thereby other stream is obtainedin which stream a ratio of a concentration (a) of one specific component(for example, R-245fa) to a concentration (b) of the other specificcomponent (for example, HF) of the stream (namely a ratio [a/b]) isincreased, that is when the ratio [a/b] is increased to [a′/b′] (whereina′/b′>a/b), the specific component (R-245fa) is said to beseparated/purified.

Further, in the present specification, the term “separate/purify” isintended to not necessarily mean perfect separation, and such term isused to include a fairly broad meaning so that it includes a concept ofso-called “concentration.” However, in one of the most preferableembodiments, the term “separate/purify” is intended to mean that amixture stream consisting substantially of two specific components issubjected to a predetermined step so that other stream is obtained whichcontains substantially only one specific component. In anotherembodiment of the most preferable embodiments, the term“separate/purify” is intended to mean that a mixture stream consistingsubstantially of two specific components and at least one component issubjected to a predetermined step so that other stream is obtained whichis substantially free from one of the specific components.

When R-245fa is separated/purified from a reaction mixture as describedabove, alkaline washing and/or water washing is usually used for theseparation of unreacted HF from R-245fa (and other HFC if any). However,separated HF in such a manner is present in an aqueous solution andthere is no other way than disposing it. Thus, the above mentionedseparation not only wastes HF but also requires additional cost forwashing and disposing. Therefore, it is desirable to provide a processof more effectively separating/purifying R-245fa and/or HF from amixture of HF and R-245fa.

As to other HFCs such as R-134a (1, 1, 1, 2-tetrafluoroethane), thereare examples in which using an azeotropic mixture of HF and the HFC,separating R-134a is separated from a mixture containing those compounds(see, for example, Japanese Patent Kokai Publication Nos. 4-261126 and5-178768). However, with respect to the separation of R-245fa and/or HFfrom a mixture of R-245fa and HF, the presence of an azeotropic mixtureof R-245fa and HF has not been known.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a process ofseparating/purifying R-245fa and/or HF from a mixture comprising atleast R-245fa and HF without a washing step as described above.

The present inventors have intensively studied the process ofseparating/purifying R-245fa and/or HF from the mixture comprising atleast R-245fa and HF, and have found for the first time that R-245fa andHF form a minimum azeotropic mixture and completed the presentinventions.

Thus, the present invention provides an azeotropic mixture consistingsubstantially of 1, 1, 1, 3, 3-pentafluoropropane and hydrogen fluoride.The azeotropic mixture is a minimum azeotropic mixture having a minimumboiling point. An azeotropic temperature and an azeotropic compositionof the azeotropic mixture depend on a pressure of a system in which theazeotropic mixture is formed. Typical azeotropic temperatures andcompositions are shown below which were measured in Example 2 which willbe described below:

Pressure Azeotropic Azeotropic Composition (kg/cm²-gauge) Temperature (°C.) (mol % of R-245fa) 2.95 40 34.5 3.50 45 40.8 4.20 50 45.0 5.80 6048.2 7.00 67 48.5 7.65 70 47.4 9.00 77 42.1 9.60 80 36.3

The above azeotropic mixture has been found for the first time by thepresent inventors.

The resulting azeotropic mixture can have a1,1,1,3,3-Pentafluoropropane/hydrogen fluoride molar ratio in a range ofabout 34.5/65.5 to about 48.5/51.5.

The azeotropic mixture can be used as reflux of a distillation step inwhich R-245fa or HF is separated/purified from a mixture comprisingR-245fa and HF. In the distillation step, the mixture containing R-245faand HF at any ratio of R245fa/HF is supplied to the distilling step as afeed, and R-245fa and HF are distilled off from the distilling step asan azeotropic mixture and a bottom product is obtained which has ahigher or lower R-245fa/HF ratio than that of the feed depending on theR245fa/HF ratio of the feed, whereby effective separation/purificationof R-245fa or HF is possible.

That is, the present invention provides a process ofseparating/purifying 1, 1, 1, 3, 3-pentafluoropropane or hydrogenfluoride in which a mixture comprising at least 1, 1, 1, 3,3-pentafluoropropane and hydrogen fluoride as a feed is subjected to adistillation step so that a distillate is obtained which comprises anazeotropic mixture consisting substantially of 1, 1, 1, 3,3-pentafluoropropane and hydrogen fluoride and a bottom product isobtained which comprises separated/purified 1, 1, 1, 3,3-pentafluoropropane or hydrogen fluoride.

The feed which can be used in the present process comprises at leastR-245fa and HF, and in a preferred embodiment, the feed consistssubstantially of R-245fa and HF. In the latter embodiment, theazeotropic mixture is substantially distilled off and R-245fa whichcontains substantially no HF or HF which contains substantially noR-245fa is obtained as a bottom product. Optionally, the feed maycontain other component such as 1, 1, 1, 3, 3-pentachloropropane, 1, 1,1, 3-tetraluoro-3-chloropropane and so on. Such other component(s) ismerely distributed to the distillate or the bottom product depending onits boiling point at an operation pressure of the distillation step andan azeotropic temperature of the other component and HF if they formanother azeotropic mixture. As a concrete example, the feed may be areaction mixture obtained upon the production of R-245fa frompentachloropropane and HF.

When a ratio of R-245fa/HF of the feed is smaller than that of anazeotropic mixture which is formed at an operation pressure of thedistillation step, a distillation bottom product comprising HF which issubstantially free from R-245fa (or which contains substantially noR-245fa) is obtained by a distillation operation in which a distillatecomprising an azeotropic mixture of R-245fa and HF is obtained, and aportion of the distillate is used as reflux.

To the contrary, when the ratio of R-245fa/HF of the feed is larger thanthat of the azeotropic mixture which is formed at the operation pressureof the distillation step, a distillation bottom product which issubstantially free from HF (or which contains substantially no HF) isobtained by a distillation operation in which the distillate comprisingthe azeotropic mixture of R-245fa and HF is obtained, and a portion ofthe distillate is used as reflux.

In the separation/purification process according to the presentinvention as described above, operation conditions are not particularlylimited, but appropriately selected depending on a feed composition, anaimed separation/purification extent, utility conditions (for example, acooling temperature of the distillate, a heating temperature at thebottom of an distillation apparatus and so on), and apparatuslimitations (for example, pressure resistance of the apparatus and soon). For example, the operation pressure may be generally in the rangebetween 1 kg/cm²-G and 30 kg/cm²-G, and preferably 1 kg/cm²-G and 20kg/cm²-G.

Based on the data of the above azeotropic compositions, it has beenfurther found for the first time that the azeotropic composition ofR-245fa and HF considerably greatly changes depending on a pressure ofthe system. According to the extensive studies of the present inventors,it has been clarified that the azeotropic phenomenon of R-245fa and HFshows a maximum value of the R-245fa/HF ratio of the azeotropiccomposition at a system pressure of about 7 kg/cm²-G, and in thevicinity of that pressure, the R-245fa/HF ratio of the azeotropiccomposition depends relatively less on the system pressure.

By using the system pressure dependency of the azeotropic phenomenon,there is provided another process in which R-245fa and/or HF isseparated/purified by processing the mixture comprising at least R-245faand HF.

That is, there is provided a process of treating a feed mixturecomprising at least R-245fa and HF, which process comprises the stepsof:

subjecting the feed mixture to a first distillation stage, whereby

a first distillate is obtained which comprises an azeotropic mixtureconsisting substantially of R-245fa and HF, and

a first bottom product is obtained which comprises R-245fa substantiallyfree from HF when an R-245fa/HF ratio (for example, a molar ratio, amole percentage of R-245fa based on sum of R-245fa and HF and so on,herein after which may be referred to as merely “ratio”) of the feedmixture is larger than the R-245fa/HF ratio of the first distillate, ora first bottom product is obtained which comprises HF substantially freefrom R-245fa when the R-245fa/HF ratio of the feed mixture is smallerthan the R-245fa/HF ratio of the first distillate, and

subjecting the first distillate to a second distillation stage which isoperated at a pressure which is different from that of the firstdistillation stage, whereby

a second distillate is obtained which comprises an azeotropic mixtureconsisting substantially of R-245fa and HF, and

a second bottom product is obtained which comprises R-245fasubstantially free from HF when the R-245fa/HF ratio of the firstdistillate is larger than the R-245fa/HF ratio of the second distillate,or a second bottom product is obtained which comprises HF substantiallyfree from R-245fa when the R-245fa/HF ratio of the first distillate issmaller than the R-245fa/HF ratio of the second distillate.

By recovering the first and/or the second bottom products, R-245faand/or HF are separated/purified. Namely, the present invention providesa process to separate/purify R-245fa and/or HF.

This process is formed by so combining in series two of theseparation/purification processes as described earlier in which a singleseparation/purification is carried out that they are carried out atdifferent operation pressures, and the distillate which comprises theazeotropic mixture and which is obtained in the firstseparation/purification process is used as a feed mixture for the secondseparation/purification process which is operated at a differentoperation pressure. It is of course possible to repeat such distillationstages more than twice, and there is no particular limitation in therepeating number. In a practical application, twice is sufficient. Thus,the above combined separation/purification process will be explainedbelow with reference to an example in which two distillation stages arecombined.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph which shows an effect of an operation pressure on acomposition of an azeotropic mixture according to the present invention;

FIG. 2 is a graph which shows an effect of an operation pressure on acomposition of an azeotropic mixture according to the present invention;

FIG. 3 is a graph which shows an effect of an operation pressure on acomposition of an azeotropic mixture according to the present invention;

FIG. 4 schematically shows a flow sheet of a preferable embodiment ofthe present invention in which R-245fa and HF are separated/purified;and

FIG. 5 is a graph which shows results of vapor-liquid equilibriummeasurement of an R-245fa/HF system.

In the drawing, each numeral indicates as follows:

1 high-pressure distillation column (first distillation stage)

3 low-pressure distillation column (second distillation stage)

5 feed comprising R-245fa/HF

7 first distillate

9 cooler

11 reflux

13 first bottom product

15 second distillate

17 cooler

19 reflux

21 second bottom product

DETAILED DESCRIPTION OF THE DRAWINGS

In the first embodiment of the combined separation/purification processas described above, it is characterized in that the R-245fa/HF ratio ofthe feed mixture is larger than the R-245fa/HF ratio of the firstdistillate and also larger than the R-245fa/HF ratio of the seconddistillate, and the R-245fa/HF ratio of the first distillate is largerthan the R-245fa/HF ratio of the second distillate.

This embodiment can be easily understood with reference to the graph ofFIG. 1 in which the azeotropic data is shown. In the graph of FIG. 1,the axis of ordinate indicates mol % of R-245fa of the azeotropicmixture of R-245fa and HF (i.e. 100×R-245fa/[R-245fa+HF], thus thiscorresponds to the R-245fa/HF ratio), and the axis of abscissasindicates pressure at which the azeotropic mixture is formed. In thefirst embodiment, the R-245fa/HF ratio of the feed mixture is indicatedby for example A. The first distillation stage is operated at forexample a pressure B, and thus the R-245fa/HF ratio of the firstdistillate is indicated by C. Since A is larger than C (i.e. A>C), thebottom product of the first distillation stage can be made substantiallyfree from HF. Then, the first distillate is subjected to the seconddistillation stage which is operated at for example a pressure of D sothat the R-245fa/HF ratio of the second distillate is E. As clearlyseen, C is larger than E (i.e. C>E), and therefore the bottom product ofthe second distillation stage can be made substantially free from HF.

In the second embodiment of the combined separation/purification processaccording to the present invention, it is characterized in that theR-245fa/HF ratio of the feed mixture is larger than the R-245fa/HF ratioof the first distillate and also larger than the R-245fa/HF ratio of thesecond distillate, and the R-245fa/HF ratio of the first distillate issmaller than the R-245fa/HF ratio of the second distillate.

Referring to the graph of FIG. 2, the second embodiment is the same asthe above first embodiment except that, in the fourth embodiment, thesecond distillation stage is operated at for example a pressure of F,and the R-245fa/HF ratio of the second distillate is then G (thus, G>C),so that the bottom product of the second distillation stage can besubstantially free from R-245fa.

In the third embodiment of the combined separation/purification processaccording to the present invention, it is characterized in that theR-245fa/HF ratio of the feed mixture is smaller than the R-245fa/HFratio of the first distillate and also smaller than the R-245fa/HF ratioof the second distillate, and the R-245fa/HF ratio of the firstdistillate is larger than the R-245fa/HF ratio of the second distillate.

This embodiment is easily understood with reference to the graph of FIG.2 which is substantially the same as the graph of FIG. 1. In the thirdembodiment, the R-245fa/HF ratio of the feed mixture is indicated by forexample H. The first distillation stage is operated at for example apressure of I, and thus since J>H, the R-245fa/H ratio of the firstdistillate is indicated by J. Therefore, the first bottom product can bemade substantially free from R-245fa. Then, the first distillate issubjected to the second distillation stage which is operated at forexample a pressure of K so that the R-245fa/HF ration of the seconddistillate is L. As clearly seen, J>L and thus the bottom product of thesecond distillate can be made substantially free from HF.

In the fourth embodiment of the combined separation/purification processaccording to the present invention, it is characterized in that theR-245fa/HF ratio of the feed mixture is smaller than the R-245fa/HFratio of the first distillate and also smaller than the R-245fa/HF ratioof the second distillate, and the R-245fa/HF ratio of the firstdistillate is smaller than the R-245fa/HF ratio of the seconddistillate.

Referring to the graph of FIG. 1, the fourth embodiment is the same asthe above third embodiment except that, in the second embodiment, thesecond distillation stage is operated at for example a pressure of M,and the R-245fa/HF ratio of the second distillate is then N (thus, N>J),so that the bottom product of the second distillation stage can besubstantially free from R-245fa.

In the fifth embodiment of the combined separation/purification processaccording to the present invention, it is characterized in that theR-245fa/HF ratio of the feed mixture is between the R-245fa/HF ratio ofthe first distillate and the R-245fa/HF ratio of the second distillate,and the R-245fa/HF ratio of the first distillate is larger than theR-245fa/HF ratio of the second distillate.

This embodiment is easily understood with reference to the graph of FIG.3 which is substantially the same as the graph of FIG. 1. In the fifthembodiment, the R-245fa/HF ratio of the feed mixture is indicated by forexample P. The first distillation stage is operated at for example apressure of Q, and thus the R-245fa/H ratio of the first distillate isindicated by R. Therefore, the first bottom product can be madesubstantially free from R-245fa. Then, the first distillate is subjectedto the second distillation stage which is operated at for example apressure of S so that the R-245fa/HF ratio of the second distillate isT. As clearly seen, R>T and thus the bottom product of the seconddistillation stage can be made substantially free from HF.

In the sixth embodiment of the combined separation/purification processaccording to the present invention, it is characterized in that theR-245fa/HF ratio of the feed mixture is between the R-245fa/HF ratio ofthe first distillate and the R-245fa/HF ratio of the second distillate,and the R-245fa/HF ratio of the first distillate is smaller than theR-245fa/HF ratio of the second distillate.

Referring to the graph of FIG. 3, in the sixth embodiment, the firstdistillation stage is operated at for example a pressure of S, and theR-245fa of the first distillate corresponds to T. Since P>T, the bottomproduct of the first distillation stage can be made substantially freefrom HF. The second distillation stage is operated at for example apressure of Q, and then the R-245/HF ratio of the second distillate is R(thus, R>T), so that the bottom product of the second distillation stagecan be made substantially free from R-245fa.

Therefore, in the separation/purification process in which thedistillation stages are combined according to the present invention, byselecting operation pressures appropriately, R-245fa which otherwisewould be distributed to the bottom product is distributed to thedistillate as the azeotropic mixture, and/or HF which otherwise would bedistributed to the distillate is distributed to the bottom product. Tothe contrary, HF which otherwise would be distributed to the bottomproduct is distributed to the distillate as the azeotropic mixture,and/or R-245fa which otherwise would be distributed to the distillate isdistributed to the bottom product.

In one preferable case of the first embodiment, when the R-245fa/HF moleratio of the feed mixture is not less than 1, the first distillationstage is operated at a pressure in the range between about 5 kg/cm²-Gand about 8 kg/cm²-G and the second distillation stage is operated at apressure not more than about 5 kg/cm²-G or not less than about 8kg/cm²-G.

In this case, since most of R-245fa of which amount is relatively largerin the feed mixture is not distilled off, but obtained as the firstbottom product of the first distillation stage, there is provided anadvantage in energy consumption. In addition, another advantage isprovided in that the smaller the R-245fa/HF ratio in the seconddistillation stage is, the smaller amount of R-245fa only has to bedistilled off in the second distillation stage (thus, a concentration ofR-245fa in the second distillate is reduced, and an amount of R-245fa isincreased which is obtained as the bottom product).

In one preferable case of the second embodiment, when the R-245fa/HFmole ratio of the feed mixture is not less than 1, the firstdistillation stage is operated at a pressure not more than about 5kg/cm²-G or not less than about 8 kg/cm²-G, and the second distillationstage is operated at a pressure in the range between about 5 kg/cm²-Gand about 8 kg/cm²-G.

In this case, since most of R-245fa of which amount is relatively largerin the feed mixture is not distilled off, but obtained as the firstbottom product of the first distillation stage, there is provided anadvantage in energy consumption.

In one preferable case of the third embodiment, when the R-245fa/HF moleratio of the feed mixture is not more than 0.4, the first distillationstage is operated at a pressure in the range between about 5 kg/cm²-Gand about 8 kg/cm²-G and the second distillation stage is operated at apressure not more than about 5 kg/cm²-G or not less than about 8kg/cm²-G.

In this case, since most of HF of which amount is relatively larger inthe feed mixture is not distilled off, but obtained as the first bottomproduct of the first distillation stage, there is provided an advantagein energy consumption.

In one preferable case of the fourth preferable embodiment, when theR-245fa/HF mole ratio of the feed mixture is not more than 0.4, thefirst distillation stage is operated at a pressure not more than about 5kg/cm²-G or not less than about 8 kg/cm²-G, and the second distillationstage is operated at a pressure in the range between about 5 kg/cm²-Gand about 8 kg/cm²-G.

In this case, since most of HF of which amount is relatively larger inthe feed mixture is not distilled off, but obtained as the first bottomproduct of the first distillation stage, there is provided an advantagein energy consumption. In addition, other advantages are provided inthat the larger the R-245fa/HF ratio of the first distillate is, thesmaller amount of HF only has to be distilled off in the firstdistillation stage (thus, a concentration of HF in the first distillateis reduced, and an amount of HF is increased which is obtained as thefirst bottom product), and that the smaller the R-245fa/HF ratio of thesecond distillate in the second distillation stage is, the smalleramount of R-245fa only has to be distilled off in the seconddistillation stage (thus, a concentration of R-245fa in the seconddistillate is reduced).

In the above cases, the second distillate may be re-used by mixing withthe feed mixture to be supplied to the first distillation stage.Further, HF obtained as the bottom product may be re-circulated to thereaction system which produces R-245fa. R-245fa obtained as the secondbottom product (and R-245fa as the first bottom product if available)may be used for other predetermined application as it is or after beingsubjected to conventional purification treatment. The applications ofthe products thus obtained in the distillation stages are generallyapplicable to other cases which will be explained below.

When the feed mixture to be supplied to the first distillation stagecontains, in addition to R-245fa and HF, other component, it is merelydistributed to the distillate or the bottom product depending on itsboiling point or its azeotropic point with HF when it forms anazeotropic mixture with HF.

In one preferable case of the fifth embodiment, when the R-245fa/HF moleratio of the feed mixture is in the range between about 0.4 and about 1,the first distillation stage is operated at a pressure in the rangebetween about 5 kg/cm²-G and about 8 kg/cm²-G and the seconddistillation stage is operated at a pressure not more than about 5kg/cm²-G or not less than about 8 kg/cm²-G.

In one preferable case of the sixth embodiment, when the R-245fa/HF moleratio of the feed mixture is in the range between about 0.4 and about 1,the first distillation stage is operated at a pressure not more thanabout 5 kg/cm²-G or not less than about 8 kg/cm²-G, and the seconddistillation stage is operated at a pressure in the range between about5 kg/cm²-G and about 8 kg/cm²-G.

The separation/purification process as described above in which thehigher pressure distillation stage and the lower pressure distillationstage are combined may be carried out under any operation conditionsmerely provided that the operation pressures are selected to provide theazeotropic compositions of the distillates which are different from eachother. It is of course possible to select more optimal operationconditions under considerations of energy consumption and facility cost.

Considering cooling conditions of the distillate and also heatingconditions at the bottom of the distillation column, it is appropriateto select the higher operation pressure and the lower operation pressurein the range between about 1 kg/cm²-G and about 30 kg/cm²-G, andpreferably between about 1 kg/cm²-G and about 20 kg/cm²-G.

The distillation stage(s) may be carried out batch-wise or continuouslywhen they are combined or when a single distillation stage is carriedout. Generally, the distillation stage(s) is preferably carried outcontinuously. There is no specific limitation as to the type of thedistillation apparatus to be used, and the conventional distillationapparatus (for example, a packed column, a plate column and so on) maybe used. Optionally, when the synthesis of R-245fa is carried out in aliquid phase reaction, the distillation apparatus may be integrated witha reactor. In one concrete embodiment, fluorination ofpentachloropropane is carried out in HF as a solvent, and R-245faproduced is distilled off from a distillation column which alsofunctions as a reactor.

BEST MODE FOR CARRYING OUT THE INVENTION

In FIG. 4, there is schematically shown a flow sheet of one embodimentof the combined higher pressure and lower pressure distillationoperations in which the first distillation stage and the seconddistillation stage are carried out at a pressure not more than about 8kg/cm²-G. This process comprises the first distillation stage 1 which isa higher pressure column and the second distillation stage 3 which is alower pressure column and continuously processes the feed mixture 5which comprises at least R-245fa and HF. The feed mixture 5 may be forexample a reaction effluent from a reaction system which producesR-245fa or may be from any other source provided that it comprisesR-245fa and HF.

The feed mixture 5 is first introduced into the higher pressure column 1(its operation pressure is for example about 7 kg/cm²-G) which isoperated so as to distill off the azeotropic mixture of R-245fa and HF,and the first distillate 7 comprising the azeotropic mixture is cooledby the cooler 9 to be condensed. A portion of the condensate is returnedto the top of the column as the reflux 11 so as to carry out the firstdistillation stage. When the R-245fa/HF ratio of the feed mixture to besupplied to the first distillation stage is smaller than the R-245fa/HFratio of the azeotropic mixture at the operation pressure of the firstdistillation stage, substantially all of R-245fa is distilled off withHF of which amount is such that it forms the azeotropic mixture with thedistilled off R-245fa, so that remaining HF which is substantially freefrom R-245fa is obtained as the bottom product 13 of the higher pressuredistillation column 1.

A remaining fraction 25 balanced with the reflux 11 returned to thedistillation column 1 is supplied to the second distillation stage 3(its operation pressure is for example about 3 kg/cm²-G) as the feedmixture. Also, the second distillation stage is operated so as todistill off the azeotropic mixture of R-245fa and HF as the seconddistillate 15. As in the first distillation stage, the second distillate15 is cooled by the cooler 17, and a portion of the cooled distillate isreturned to a top of the column as the reflux 19. Since the seconddistillation stage is at the operation pressure which is lower than thatof the first distillation stage, the R-245fa/Hf ratio of the seconddistillate is smaller than that of the first distillate so thatsubstantially all HF is distilled off with R-245fa of which amount formsthe azeotropic mixture with the substantially all HF. Thus R-245fa whichis substantially free from HF is obtained from the bottom product 21.

The R-245fa/HF mixture 23 which is balanced with the reflux 19 may berecycled to the feed mixture 5 to be supplied to the first distillationstage 1 as shown. Alternatively, since the mixture contains much less HFrelatively to the feed mixture 5, HF is removed from the mixture by theconventional treatment such as alkaline washing or water washing so thatR-245fa may be recovered.

In this embodiment, since most of HF of which amount in the feed mixtureis relatively large is not distilled off but obtained as the firstbottom product 13 of the first distillation stage 1, there is providedan advantage as to the energy consumption. Further advantages are inthat when the operation pressure of the first distillation stage ishigher, less amount of HF has to be distilled off in the firstdistillation stage (and thus a concentration of HF of the firstdistillate 7 is reduced, and also an amount of HF obtained as the firstbottom product is increased), and that when the operation pressure ofthe second distillation stage is lower, a less amount of R-245fa onlyhas to be distilled off in the second distillation stage 3 (and thus aconcentration of R-245fa of the second distillate 15 is reduced, andalso an amount of R-245fa as the second bottom product 21 is increased).

Since the pressure dependency of the azeotropic phenomenon of theR-245fa and HF shows a maximal point, there are two different operationpressures which provide the same azeotropic composition. Thus,alternatively, it is possible to operate either or both of thedistillation stages at the higher operation pressure which distills offthe same azeotropic mixture as the lower operation pressure. Forexample, the first distillation stage is operated at a pressure of about7 kg/cm²-G and the second distillation stage is operated at a pressureof about 10 kg/cm²-G. Also, the contrary manner to the above embodimentsmay be used (i.e. it is possible to operate either or both of the firstand the second distillation stages at an operation pressure higher thanabout 8 kg/cm²-G). Therefore, any of the following embodiments may becarried out: The both of the distillation stages are carried out at anoperation pressure lower than about 8 kg/cm²-G; the both of thedistillation stages are carried out at an operation pressure higher thanabout 8 kg/cm²-G; and one of the distillation stages is carried out atan operation pressure higher than about 8 kg/cm²-G, and the other iscarried out at an operation pressure lower than about 8 kg/cm²-G.

The present process which treats a feed mixture having the R-245fa/HFratio higher than that of the azeotropic mixture formed at the operationpressure of the first distillation stage (which feed mixture is referredto as feed mixture 5′) may be carried out using, for example, apparatuswhich comprises a lower pressure distillation column (its operationpressure is for example 3 kg/cm²-G) as the first distillation stage 1′,and a higher pressure distillation column (its operation pressure is forexample 7 kg/cm²-G) as the second distillation stage 3′.

The feed mixture 5′ is first introduced into the lower pressuredistillation column 1′, and the first distillation stage is carried outin which an azeotropic mixture 7′ is distilled off, and cooled andcondensed by a cooler 9′ and a portion of the condensate is returned toa top of the column as reflux 11′. Since the R-245fa/HF ratio of thefeed mixture to be supplied to the first distillation stage is largerthan that of the azeotropic mixture formed at the operation pressure ofthe first distillation stage, substantially all HF which is supplied tothe first distillation stage is distilled off with R-245fa of whichamount corresponds to an amount required to form the azeotropic mixturewith the substantially all HF, and the rest of R-245fa is obtained asthe bottom product 13′ which is substantially free from HF.

The remaining fraction 25′ which is obtained by subtracting the reflux11′ from the first distillate 7′ is supplied to the second distillationstage 3′ as a feed mixture. Also, in the second distillation stage, anazeotropic mixture is distilled off from a top of the column as thesecond distillate 15′. As in the first distillation stage, thedistillate is cooled by the cooler 17′ and a portion of the cooleddistillate is returned to a top of the column as reflux 19′. Further,the second bottom product 21′ comprising HF which is substantially freefrom R-245fa is obtained from the bottom of the second distillationstage 3′.

In this embodiment, since the first distillation stage 1′ is operated atan operation pressure lower than the second distillation stage 3′, aconcentration of HF of the azeotropic mixture 7′ distilled off from thefirst distillation stage is larger than a concentration of HF of theazeotropic mixture 15′ distilled off from the second distillation stage.Since such R-245fa/HF mixture 25′ is supplied to the second higherpressure distillation stage 3′, substantially all R-245fa which issupplied to the second distillation stage is distilled off so as to formthe azeotropic mixture with HF, whereby the bottom product 19 of thesecond distillation stage is substantially free from R-245fa.

In this embodiment, since most of R-245fa of which amount is relativelylarge is not distilled off but obtained as the first bottom product 13′of the first distillation stage 1′, there is provided an advantage as tothe energy consumption. Further advantages are in that when theoperation pressure of the first distillation stage is lower, a lessamount of R-245fa only has to be distilled off in the first distillationstage (and thus a concentration of R-245fa of the first distillate 7′ isreduced, and also an amount of R-245fa obtained as the first bottomproduct 13′ is increased), and that when the operation pressure of thesecond distillation stage 3′ is higher, a less amount of HF only has tobe distilled off in the second distillation stage (and thus aconcentration of HF of the second distillate 15′ is reduced, and also anamount of HF obtained as the second bottom product 21′ is increased).

As in the above explanation, it is also possible to utilize thatdistillates having the same compositions may be obtained at differentoperation pressures based on the azeotropic phenomenon of the R-245fa/HFsystem showing the maximal point in the pressure dependency.

Effects of the Invention

By the process of separating/purifying R-245fa according to the presentinvention in which the distillation employing the azeotropic mixture ofthe present invention is used, R-245fa or HF is effectivelyseparated/purified even without the conventional alkaline washing orwater washing, and separated/purified HF may be re-used or used forother application.

Further, when the present invention is carried out with combining twodistillation stages operated at different pressures, HF and R-245fa areeffectively separated/purified.

EXAMPLES Example 1 Measurement of Vapor-liquid Equilibrium of R-245faand HF

R-245fa and HF were charged in a bomb at a predetermined ratio, and aliquid phase sample and a vapor phase sample were obtained after thesystem reached the vapor-liquid equilibrium. As to concentrations ofR-245fa and HF, the samples were analyzed.

The analysis results (concentrations of R-245fa in mol % of the liquidphase and the vapor phase) are shown below (the balances areconcentrations of HF):

Pressure Liquid Phase Vapor Phase Temp. (° C.) (kg/cm²-G) (mol %) (mol%) 50 3.50 9.5% 30.5% 50 4.05 24.2% 40.1% 50 4.20 38.7% 42.8% 50 4.1556.1% 45.0% 50 3.55 76.5% 51.3% 50 2.60 90.0% 65.0%

The above results are shown in the graph of FIG. 5. As obviously seenfrom FIG. 5, the R-245fa/HF system has the azeotropic point. In the caseas shown, the azeotropic temperature is 50° C., the azeotropic pressureis 4.2 kg/cm²-G, and the azeotropic composition was R-245fa (45 mol%)/HF (55 mol %).

Example 2 Relationship Between Pressure and Azeotropic Composition

The pressure of the R-245fa/HF system was variously changed by changingthe temperature of the system similarly to Example 1, and the azeotropictemperature and the azeotropic composition (mol % of R-245fa) at eachpressure were measured. The results are shown in Table below and also inFIGS. 1 to 3:

Pressure Azeotropic Liquid & Vapor (kg/cm²-G) Temp. (° C.) Phases (mol%) 2.95 40 34.5% 3.50 45 40.8% 4.20 50 45.0% 5.80 60 48.2% 7.00 67 48.5%7.65 70 47.4% 9.00 77 42.1% 9.60 80 36.3%

It is seen from the above results, the azeotropic composition of theR-245fa/HF system greatly depends on the system pressure.

1. A process of separating or purifying 1,1,1,3,3-pentafluoropropane inwhich a mixture comprising at least 1,1,1,3,3-pentafluoropropane andhydrogen fluoride is subjected to a distillation step so that adistillate is obtained which comprises an azeotropic mixture consistingessentially of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride,wherein under a pressure in a range of 2.95 kg/cm²-gauge to 9.60kg/cm²-gauge, at a temperature of about 40° C. to about 80° C., theazeotropic mixture has a 1,1,1,3,3-pentafluoropropane/hydrogen fluoridemolar ratio in a range of about 34.5/65.5 to about 48.5/51.5, and abottom product is obtained which comprises 1,1,1,3,3-pentafluoropropanesubstantially free from hydrogen fluoride.
 2. A process of separating orpurifying hydrogen fluoride in which a mixture comprising at least1,1,1,3,3-pentafluoropropane and hydrogen fluoride is subjected to adistillation step so that a distillate is obtained which comprises anazeotropic mixture consisting essentially of1,1,1,3,3-pentafluoropropane and hydrogen fluoride, wherein under apressure in a range of 2.95 kg/cm²-gauge to 9.60 kg/cm²-gauge, theazeotropic mixture has a temperature of about 40° C. to about 80° C. andhas a 1,1,1,3,3-pentafluoropropane/hydrogen fluoride molar ratio in arange of about 34.5/65.5 to about 48.5/51.5, and a bottom product isobtained which comprises hydrogen fluoride substantially free from1,1,1,3,3-pentafluoropropane.
 3. A process of treating a feed mixturecomprising at least 1,1,1,3,3-pentafluoropropane and hydrogen fluoride,which process comprises the steps of: subjecting the feed mixture to afirst distillation stage, whereby a first distillate is obtained whichcomprises an azeotropic mixture consisting essentially of1,1,1,3,3-pentafluoropropane and hydrogen fluoride, wherein under apressure in a range of 2.95 kg/cm²-gauge to 9.60 kg/cm²-gauge, theazeotropic mixture of the first distillate has a temperature of about40° C. to about 80° C. and a 1,1,1,3,3-pentafluoropropane/hydrogenfluoride molar ratio in a range of about 34.5/65.5 to about 48.5/51.5,and a first bottom product is obtained which comprises1,1,1,3,3-pentafluoropropane substantially free from hydrogen fluoridewhen a 1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratio of the feedmixture is larger than the 1,1,1,3,3-pentafluoropropane/hydrogenfluoride ratio of the first distillate, or a first bottom product isobtained which comprises hydrogen fluoride substantially free from1,1,1,3,3-pentafluoropropane when the1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratio of the feed mixtureis smaller than the 1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratioof the first distillate, and subjecting the first distillate to a seconddistillation stage which is operated at a pressure which is differentfrom that of the first distillation stage, whereby a second distillateis obtained which comprises an azeotropic mixture consisting essentiallyof 1,1,1,3,3-pentafluoropropane and hydrogen fluoride, wherein under apressure in a range of 2.95 kg/cm²-gauge to 9.60 kg/cm²-gauge, theazeotropic mixture of the second distillate has a temperature of about40° C. to about 80° C. and a 1,1,1,3,3-pentafluoropropane/hydrogenfluoride molar ratio in a range of about 34.5/65.5 to about 48.5/51.5,and a second bottom product is obtained which comprises1,1,1,3,3-pentafluoropropane substantially free from hydrogen fluoridewhen the 1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratio of thefirst distillate is larger than the1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratio of the seconddistillate, or a second bottom product is obtained which compriseshydrogen fluoride substantially free from 1,1,1,3,3-pentafluoropropanewhen the 1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratio of thefirst distillate is smaller than the1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratio of the seconddistillate.
 4. The process according to claim 3, wherein the1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratio of the feed mixtureis larger than the 1,1,1,3,33-pentafluoropropane/hydrogen fluoride ratioof the first distillate and also larger than the1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratio of the seconddistillate, and the 1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratioof the first distillate is smaller than the1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratio of the seconddistillate.
 5. The process according to claim 4, wherein the firstdistillation stage is operated at a pressure in the range between 1kg/cm²-G and 4 kg/cm²-G or in the range between 8 kg/cm²-G and 20kg/cm²-G, and the second distillation stage is operated at a pressure inthe range between 4 kg/cm²-G and 8 kg/cm²-G.
 6. The process according toclaim 3, wherein the 1,1,1,3,3-pentafluoropropane/hydrogen fluorideratio of the feed mixture is smaller than the1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratio of the firstdistillate and also smaller than the1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratio of the seconddistillate, and the 1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratioof the first distillate is larger than the1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratio of the seconddistillate.
 7. The process according to claim 6, wherein the firstdistillation stage is operated at a pressure in the range between 4kg/cm²-G and 8 kg/cm²-G, and the second distillation stage is operatedat a pressure in the range between 1 kg/cm²-G and 4 kg/cm²-G or in therange between 8 kg/cm²-G and 20 kg/cm²-G.
 8. The process according toclaim 3, wherein the 1,1,1,3,3-pentafluoropropane/hydrogen fluorideratio of the feed mixture is between the1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratio of the firstdistillate and the R-1,1,1,3,3-pentafluoropropane/hydrogen fluorideratio of the second distillate, and the1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratio of the firstdistillate is larger than the 1,1,1,3,3-pentafluoropropane/hydrogenfluoride ratio of the second distillate.
 9. The process according toclaim 8, wherein the first distillation stage is operated at a pressurein the range between 4 kg/cm²-G and 8 kg/cm²-G, and the seconddistillation stage is operated at a pressure in the range between 1kg/cm²-G and 4 kg/cm²-G or in the range between 8 kg/cm²-G and 20kg/cm²-G.
 10. The process according to claim 3, wherein the1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratio of the feed mixtureis between the 1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratio ofthe first distillate and the 1,1,1,3,3-pentafluoropropane/hydrogenfluoride ratio of the second distillate, and the1,1,1,3,3-pentafluoropropane/hydrogen fluoride ratio of the firstdistillate is smaller than the 1,1,1,3,3-pentafluoropropane/hydrogenfluoride ratio of the second distillate.
 11. The process according toclaim 10, the first distillation stage is operated at a pressure in therange between 1 kg/cm²-G and 4 kg/cm²-G or in the range between 8kg/cm2-G and 20 kg/cm²-G, and the second distillation stage is operatedat a pressure in the range between 4 kg/cm²-G and 8 kg/cm²-G.